This invention relates generally to methods of manufacture of nanostructured materials. More particularly, this invention relates to methods of manufacture of nanostructured metals, metal carbides, and metal alloys by thermochemical and sonochemical decomposition, as well as by reduction. These synthetic schemes use readily available starting materials, of relatively low cost.
Metals, metal carbides, and metal alloys are traditionally produced by melting and casting techniques which entail some level of microstructural and chemical inhomogeneities. Recent developments in rapid solidification techniques, such as powder atomization and melt spinning, are capable of producing chemically homogeneous materials with fine microstructures. Grain sizes in micrometers are achievable by rapid solidification techniques. The microstructural refinement is usually accompanied by enhanced mechanical and physical properties. In recent years, much attention has been devoted to a further reduction of grain size from the micrometer size to the nanometer. Nanostructured materials have superior mechanical, magnetic, and other physical properties.
In particular, iron and iron-based alloys are technologically important materials in modem industry. Ultrafine iron dispersions have applications in ferrofluids, magnetic memory systems and catalysis. M50 steel (4.0% Cr, 4.5% Mo, 1.0% V, 0.8% C, with balance of Fe by weight), because of its good resistance to tempering, wear and rolling contact fatigue, has been used extensively in the aircraft industry as main-shaft bearings in gas-turbine engines. In the hardened condition, M50 steel consists of a body-centered tetragonal martensite phase and a dispersion of carbide particles including M.sub.23 C.sub.6 M.sub.6 C, M.sub.2 C and MC. The grain size of the martensite is about 0.032 mm and smaller, and some of the dispersion particles are several microns in diameter. These relatively large carbide particles often act as fatigue crack initiation sites. A nanostructured M50 steel would not contain these large carbide particles. Furthermore, a nanostructured M50 steel may have improved resistance to tempering, and wear and rolling contact fatigue.
Techniques for the production of nanostructured materials include physical methods such as gas-phase condensation, metal evaporation, spray pyrolysis, laser ablation, and plasma synthesis. Chemical methods include sol-gel synthesis, electrolytic deposition, chemical vapor deposition, and laser pyrolysis. Chemical synthesis is advantageous in that it allows tailored synthesis through assembly of atomic or molecular precursors, enhanced control of stoichiometry, and mixing of constituent phases at the molecular level. Chemical synthesis are also superior in providing for faster, cost-effective production of bulk quantities of materials.
Examples of the chemical synthesis of ultrafine iron and iron-cobalt alloys have been described in U.S. Pat. No. 4,842,641 issued to Gonsalves; by Jaques van Wonterghem et al in an article entitled "Formation of a Metallic Glass by Thermal Decomposition of Fe(CO).sub.5 " in Physical Review Letters, Vol. 55, No. 4, pages 410-413 (1985); by Jaques van Wonterghem et al in an article entitled "Formation of Ultrafine Amorphous Alloy Particles by Reduction in Aqueous Solution" in Nature, Vol. 322, pages 622-623 (1986); and by Kenneth E. Gonsalves and Kuttaripalyam T. Kembaiyan in an article entitled "Synthesis of Advanced Ceramics and Intermetallics From Organometallic/Polymeric Precursors" in Solid State Ionics, 32/33, pages 661-668 (1989). However, there are no previous reports of the chemical synthesis of a multicomponent commercial nanostructured M50 steel.